Justin Martyr on Baptism and the Eucharist

 St. Justin Martyr (d. AD 165) explained that before receiving the Eucharist, a person not only needed to be baptized, but also had to assent to the Catholic teaching. He writes:

But we, after we have thus washed him who has been convinced and has assented to our teaching, bring him to the place where those who are called brethren are assembled, in order that we may offer hearty prayers in common for ourselves and for the baptized [illuminated] person, and for all others in every place, that we may be counted worthy, now that we have learned the truth, by our works also to be found good citizens and keepers of the commandments, so that we may be saved with an everlasting salvation. …

And this food is called among us Εὐχαριστία [the Eucharist], of which no one is allowed to partake but the man who believes that the things which we teach are true, and who has been washed with the washing that is for the remission of sins, and unto regeneration, and who is so living as Christ has enjoined. For not as common bread and common drink do we receive these; but in like manner as Jesus Christ our Saviour, having been made flesh by the Word of God, had both flesh and blood for our salvation, so likewise have we been taught that the food which is blessed by the prayer of His word, and from which our blood and flesh by transmutation are nourished, is the flesh and blood of that Jesus who was made flesh. ( First Apology, 65, 66)

I found this at Called to Communion  http://www.calledtocommunion.com/2012/05/too-catholic-to-be-catholic-a-response-to-peter-leithart/